1. Field of the Invention
This invention relates to a filter. More particularly, this invention relates to a cartridge type clarifying filter.
2. Description of Prior Arts
The clarifying filter is a device for collecting solid particles suspended in a dilute slurry and, as such, finds utility in a wide variety of applications such as for filtration of water or drinking water, for filtration of products in the pharmaceutical industry, for filtration of fuel and lubricant oils, for filtation of electroplating liquid, and for recovery of solvents.
The performance of this filter hinges heavily on the quality and composition of the filter medium used therein. For example, woven fabric, filter paper, felt, non-woven fabric, paper pulp and fibrous materials coated with finely powdered inorganic substances which are most popularly used as filter media are inexpensive but lack the strength required in withstanding the pressure of filtration or the mechanical wear. Further, most of them lack the stability required in resistance to acids and alkalis and have no sufficient ability to resist to heat. Generally then are discarded after short periods of service because of the phenomenon of clogging. Thus, they are not economical.
Plastic membranes containing fine pores uniform in diameter are convenient filter media in the sense that they are easy of production. Similarly to those fibrous materials mentioned above, however, they have a disadvantage that their stability to resist to chemicals and heat is not sufficient. For the purpose of elminating this drawback, filter media using fluorine resins such a tetrafluoroethylene resin (Teflon by trademark designation), for example, have been developed. These new filter media still suffer from a disadvantage that they are not readily wetted with water and, therefore, offer much resistance to passing water and, what is more, they are expensive.
Recently, sintered metals also have come to be used as filter media. Such sintered metals, however, cannot be expected to provide the phenomenon of interstitial crosslinking of those solid particles desired to be separated from the dilute slurry under treatment becuase their crystal particles have a spheric shape. They are, consequently, required to retain their pores in a particularly small diameter. As filters, they offer great resistance to passing water and suffer from heavy clogging.
Porous ceramic articles such as, for example, calcined articles of diatomaceous material are also in use as filter media. Although these ceramic articles predominantly use natural raw materials and incorporate various additives suitably, their sintering is based on the self-sintering of porous particulate raw materials. The desired control of pore diameter, therefore, is difficult. The porous ceramic articles possess no sufficient strength because their backbone particles are porous by nature, because the diatomaceous earth as the main raw material which is a mineral produce of nature has its SiO.sub.2 content, alkali metal oxides content and alkaline earth metal oxides content in variable proportions and yields an inconsistent effect upon the produced ceramic, and further because any porous article obtained by the self-sintering process has its own limit to the extent to which the wetting property is enhanced by mutual contact.
In the circumstance, the desirability of developing a filter medium which enjoys high durability, excels in stability to resist heat and chemicals, offers only low resistance to passing water, and possesses an ability to provide thorough collection of solid particles desired to be separated from a given dilute slurry has been finding growing recognition.
Then, for the purpose of providing a filter with a wide area of filtration, there may be conceived an idea of designing a filter element incorporating therein a multiplicity of filter leaves (or cylindrical filter units). When fibrous materials or plastic membranes are used as filter leaves, for example, they inevitably require use of suitable supporting means. When the filter leaves are formed of ceramic material, they mever permit ample reduction in size because of their limited strength.
In is, therefore, an object of this invention to provide a novel filter.
Another object of this invention is to provide a filter which enjoys high durability, excels in stability to resist heat and chemicals, offers only low resistance to passing water, possesees an ability to provide thorough collection of solid particles desired to be separated from a given dilute slurry, and enables its filter units to be easily backwashed and replaced.